Broadband structures for waveguide hybrid tee&#39;s



March 26, 1968 R. M. WALKER BROADBAND STRUCTURES FOR WAVEGUIDE HYBRID 'IQEE'S Filed June 6, 1966 4 Sheets-Shet 1 PRIOR ART PRIOR ART fi'z'kard I12. lDa/ker buenfvr W PRIOR ART March 26, 1968 R. M. WALKER BROADBAND STRUCTURES FOR WAVEGUIDE HYBRID TEE'S Filed June 6, 1966 2 l ii/ it i L fii' eba rd 112. Walker by @MW March 26, 1968 R. M. WALKER BROADBAND STRUCTURES FOR WAVEGUIDE HYBRID TEE'S 4 Sheets-Sheet 5 Filed June 6, 1966 3 8 ozw30mmm HMSA I OQm .flz enfur m,-

3,375,472 BROADBAND STRUCTURES FOR WAVEGUIDE HYBRID TEE'S Filed June 6, 1966 March 26, 1968 v R. M. WALKER 4 Sheets-Sheet 4 aMsA' m'i'bard 1 22. Il a/AP! United States Patent 3,375,472 BROADBAND STRUCTURES FOR WAVEGUIDE HYBRID TEES Richard M. Walker, Chestnut Hill, Mass., assignor to Microwave Associates, Incorporated, Burlington, Mass, a corporation of Massachusetts Filed June 6, 1966, Ser. No. 555,529 13 Claims. (Cl. 33311) This invention relates to improvements in hybrid tee junctions in rectangular RF waveguides, and more particularly to such junctions having E-plane, H-plane and common output arms extending from a common junction region whose common output arms are folded or bent in the H-plane.

In prior art folded tee junctions, impedance matching of H-plane and E-plane arms to the common output arms has been largely obtained by the use of waveguide matching sections. These waveguide matching sections have been much more frequency sensitive than the standard waveguide connecting to the junction. In accordance with the present invention inductive posts are used to match the E-arm while controlling the geometry of a reflecting end wall of the junction to match the H-arm. Elimination of the prior art waveguide matching sections makes the relative change of impedance with frequency in the junction region the same as that for standard waveguide.

Thus it is an object of the present invention to define RF waveguide folded tee junctions with frequency re sponse characteristics matching those of standard waveguide.

A further object is to define novel means for matching H-plane and E-plane arms to common arms in an RF waveguide folded tee junction.

A further object is to define a broadband H-plane folded tee junction.

Still a further object is to define a broadband H-plane folded tee junction in which the H-plane and E-plane branch arms are aligned along a single or parallel axes.

Further objects and features of the present invention will become apparent upon reading the following specification together with the drawings in which:

FIG. 1 is a perspective view of a prior art magic tee;

FIG. 2 is a perspective view of a prior art H-plane folded tee;

FIG. 3 is a plan view of the tee of FIG. 2;

FIG. 4 is a perspective view of a second prior art embodiment of an H-plane folded tee;

FIG. 5 is a plan view of the tee of FIG. 4;

FIG. 6 is a perspective view of a prior art magic tee with transformer matching of the arms in the H-plane;

FIG. 7 is a perspective view of an H-plane folded tee according to the invention;

FIG. 8 is a sectional view of FIG. 7;

FIG. 9 is a plan view of the FIG. 8 folded tee;

FIG. 10 is a perspective view of a second embodiment of an H-plane folded tee;

FIG. 11 is a sectional view of FIG. 10;

FIG. 12 is a plan view of the FIG. 10 folded tee;

FIG. 12 is a frequency vs. VSWR graph for the H- plane folded tees of FIG. 2 andFIG. 7; and,

FIG. 14' is a frequency vs. VSWR graph for the H- plane folded tees of FIG. 4 and FIG. 10.

In order to describe the improvement structures of the present invention it is necessary todescribe the operation of the basic magic tee and hybrid tee devices to which they can be applied as follows:

(1) A conventional magic tee in rectangular waveguide is the original hybrid tee junction. This device consists of an H-plane tee and an E-plane tee superimposed to use two common waveguide output arms and to form a four terminal-pair junction. An example of the magic tee is illustrated in FIG. 1 having an H-plane arm 10, an E-plane arm 11 and collinear common output arms 12 and 13. Further description can be found in Microwave Transmission Circuits, Ragan, McGraw-Hill Boo-k Company, Inc. (1948), p. 706, FIG. 10100a.

(2) The so-called H-plane folded tee hybrid form of magic tee (Patent No. 2,840,787) is formed by folding or bending the two common waveguide output arms in the H-plane to form parallel arms. This structure provides a smaller device which is more practical in microwave circuits. An example of the H-plane folded tee hybrid is illustrated in FIGS. 2-3 with the folded output arms designated 15 and 16.

(3) Patent No. 3,192,489 issued to the present inventor jointly with Nicholas P. Kernweis describes an H-plane hybrid tee junction with further reduction in size and increased utility in microwave circuits. This is accomplished by making the E- and H-arm parallel and extending from opposite surfaces of the structure. They can be essentially on the same axis. The common output arms are disposed in a plane perpendicular to the E- and H- arm axes. This device isan H-Plane Orthogonal Hybrid Tee and an example is illustrated in FIGS. 4-5 with the H-arm designated 17 and the other arms being disposed similarly to the respective arms in FIGS. 2-3 and bearing the same reference designations.

The waveguide hybrids described in FIGS. 1 through 5 function in a similar manner. Power fed into the E- plane arm divides into two equal components out of phase in the parallel (or collinear) output arms and leakage into the H-arm is essentially zero. Power fed into the H-plane arm divides into two equal components with 0 phase difference in the parallel (or collinear) output arms and leakage into the E-plane arm is essentially zero. Power fed into either output arm divides into two equal components in the E- and H-arms and leakage into the other output arm is essentially zero if the structure is matched symmetrically (VSWR looking into any arm with the other three terminated is low). It will be recognized that the designation output arm is one of conventional usage and that input signals can be and frequently are applied to the output arms. Precise power division and complete leakage elimination (isolation) are provided by accurate mechanical symmetry in the structure.

Waveguide hybrids are used in many microwave'devices which include balanced mixers, duplexers, diplexers, power dividers, phase shifters, bridge circuits, balanced modulators and image rejection mixers. In nearly all applications the hybrid must be matched looking into each arm when each remaining arm is terminated in its characteristic impedance. Practical VSWR limits range from 1.10 to 1.80 depending on the particular application. Previous waveguide hybrid tees have been limited to a 12 to 20% of center frequency useful frequency range due to matching problems. In broadband applications it is desirable to cover the useful frequency range of standard rectangular waveguide which is 40 to 50%. The present invention describes structures which will accomplish this goal.

Several conditions must be met in order to accomplish broadband matching. The impedance of the two output arms seen from either input arm must equal the characteristic impedance of the input arm. Looking into the E- arm in FIGS. 1 through 5 the two common output arms are seen in series or an impedance equal to Z -I-Z therefore it Z =Z /2Z (Z being the impedance of the E- arm) matching is accomplished in the E-arm; where Z is the impedance of the first output arm and Z is the impedance of the second output-arm. In devices of the type herein described, all arms meet'in a common junction which is referred to herein only as the junction. Looking into the H-arm of FIGS. 1 through the two output arms are seen in parallel or an input impedance equal to Z Z /(Z +Z Therefore, if Z =Z =2Z (Z being the impedance of the H-arm) matching is accomplished in the H-arm.

The waveguide hybrid tees discussed in the preceding paragraphs and shown in FIGS. 1 through 5 use lumpedconstant irises 18, 20, 21, 22 and 23, posts 24 and buttons 19 for minor resistive and reactive matching over to frequency ranges. Typical matching structures are indicated in the figures. The major portion of impedance matching in the junction is performed by waveguide matching sections as indicated in FIG. 5 with dimensions c and d. This is a section of double waveguide (dimension 0) approximately A wavelength in length (dimension d).

FIG. 6 illustrates the technique of matching the magic tee with waveguide impedance transformers. At the junction, the common output arms are one-half standard waveguide height. Quarter-wave transformers to standard height are added to the two common output arms and the H-arm. A capacitative button 19 and post 24 are added to balance junction reactances. The magic tee of FIG. 6 is matched over a 20% frequency range but has not been used extensively because of high manufacturing cost. Bandwidth is limited by the junction reaetance matching structure. In referring to standard height waveguides, height is defined as used herein to be the dimension along which the electric field intensity is uniform and standard height is defined as the height representing the impedance characteristic of the E-arrm.

FIGS. 7 through 12 illustrate two basic embodiments of the present invention. In FIG. 7 a broadband folded tee junction is depicted with the H-arm 10 and the folded common output arms 15 and 16 all lying in a common plane and the E-arm 11 forming a common junction with arms 10, 15 and 16 along an axis perpendicular to said plane. As depicted, the arms lying in a common plane are all half-height waveguide relative to standard height waveguide in the E-arm. Arms 10, 15 and 16 may be connected to standard waveguide by the use of transforming sections as depicted in FIG. 6. The use of half-height waveguide is not critical and is given only as exemplary means of matching the E-arrn impedance to the output arms.

In specific embodiments of the invention the junctions were designed for use with .900 .400 inch standard waveguide and the waveguide dimensions in the half-height waveguide arms are .900 and .200 inch.

FIG. 8 shows the E-arm 11 with a narrow dimension b and common output arms 15 and 16 with a height dimension of b/ 2. Arms 15 and 16 each have a large dimension a (width) which is preferably equal to the width of the E-arm. A septum divides the two output arms 15 and 16 forming a common dividing wall. However arms 15 and 16 need not be folded completely parallel. When arms 15 and 16 diverge, common wall 25 would suitably be split into two separate walls one for each of the output arms. It will 'be understood that the parallel folded arms illustrated are more compact and thus generally more desirable.

Four inductive posts 26, 27, 28 and 29 are positioned across the height of the junction. The positioning of these posts is better illustrated in FIG. 9 which is a plan view of the junction viewed from the top of FIG. 7. Inductive posts 26 through 29 are suitably made of conductive pins about A inch in diameter making direct electrical connection across the height of the junction. Posts 26 and 28 form a first pair on one side of aperture 30 where E-arm 11 connects to the junction and posts 27 and 29 form a second pair positioned symmetrically on the opposite side of aperture 30.

A resonant iris 31 is positioned in the aperture 30 where the E-arm meets the junction. This iris helps prevent interaction of the E-arm aperture with energy propagating from H-arm 10.

The locations of posts 26 to 29, inclusive, are preferably on curves determined according to the teachings of my US. Patent No. 3,072,870, for I-I-plane bends, of the kind shown in FIG. 2 of that patent. Referring to FIG. 9 of the present application, one can visualize the locus of a curved line drawn from sidewall 32 (at the junction thereof with a transverse line (not shown) running through the junction of the septum 25 and the nearer short opening of the E-plane arm 11) through posts 28 and 26 and thence to the mid-point of the short side of the E-plane arm opening nearer to the H-plane arm, and thence through posts 27 and 29 to the other sidewall 33 (where the latter meets said transverse line). An example of such a locus is shown in FIG. 12. Looking now at the two output arms 15 and 16, it is apparent that those arms may be viewed as terminals of two confronting zero-radius waveguide bends, making one bend of if we can visualize a curved waveguide wall in said locus. Visualizing one only of these 90 bends, it will be understood that the arcuate line passing through posts 28 and 26, for example, is preferably located according to FIG. 2 of my Patent No. 3,072,870. That is, posts 28 and 26 are preferably located on an are curved on a constant radius longer than the wide dimension a of output arm 15 and centered at a point on a line bisecting the angle between the junction planes of the bend such that the portion of that radius within the bend along said bisecting line is approximately 0.925 of a. The junction planes of the band are the planes A-A and BB which are schematically indicated in FIG. 1 of my said patent. Similarly, for the 90 waveguide bend including posts 27 and 29 and having a junction plane confronting the first bend (along a line extended from the septum 25) and a junction plane at the second output arm 16, posts 27 and 29 are preferably located on an arc curved on a constant radius larger than a of the output arm 16 and centered at a point on a line bisecting the angle between the junction planes such that the portion of that radius within the bend along said bisecting line is approximately 0.925 of a. This preferred location of the posts 28 and 26 on the one hand, and posts 27 and 29 on the other, is thus in the locus of the curved outer wall of a bend as described in claim 14 of my Patent No. 3,072,870. I have determined that using two posts, as shown, in each 90 bend, provides the electrical equivalent of the solid curved wall of 23.2 shown in FIG. 2 of Patent No. 3,072,870. Thus energy propagating into the junction of FIG. 9 herein from the E-arm 11 divides into two equal and out of phase components, one guided in a 90 bend by posts 26 and 27 to output arm 15 and the other guided in a 90 bend by posts 28 and 29 to output arm 16.

One arrangement of the inductive posts that provides excellent VSWR characteristics is with posts 26 and 28 positioned approximately equal distances from the ends of an are as described above, and slightly closer to each other than the distance from either end. A convenient approximation is to locate post 26 at the intersection of such an arc and the center-line or axis of output waveguide 15, and to locate post 28 at the intersection of such an arc and a transverse line passing through the axis of E-arm 11 extended into the junction space. Similar considerations may be applied to posts 27 and 29. It will be understood more than two posts may be used in each bend, if desired.

Matching of the H-arm to the junction is due largely to the dimensional configuration in which it connects. In FIGS. 7 to 9 the H-arm joins the junction in the same plane as the common output arms. H-arm 10 has an aperture connection with the junction at aperture 35 in end wall 36 of the junction. End wall 36 is suitably spaced from a cross-axis through the center of E-arm aperture 30 by a distance d approximately equal to one-half the wide dimension of standard waveguide. Adjustments of this dimension d can be used for tuning. Other impedance matching means such as described previously can also be.

matching.

used in any conventional combination. Irises, posts, buttons and waveguide height variations as depicted for example in FIGS. 1 through 6 are all applicable.

FIGS. 10 to 12 depict an embodiment in which the H- arm joins the junction along an axis perpendicular to the plane of the common output arms. In FIG. 10, H-arm 17 is depicted as extending below the junction. End wall 37 of the junction opposite common output arms 15 and 16 comprises a three-section wall for matching the H-arm. This three-section end wall can be made in the form of a three-section plunger with the three sections either adjustable or fixed relative to each other.

FIG. 11 depicts a cross-section looking into the output arms of FIG. 10. Posts 26 to 29 and septum are essentially the same as in FIG. 8. H-arm 17 is illustrated in FIG. 11 projecting downward from the junction and having its long cross-sectional dimension parallel with the long cross-sectional dimension of the common arms 15 and 16 and perpendicular to the long cross-sectional dimension of E-arm 11.

FIG. 12 is a plan view looking down on FIG. 10. Posts 26 through 29 are shown positioned on an arc swung from the center of short side 38 of the E-arm aperture 30, but this is not the preferred configuration, since it will not yield as good VSWR characteristics as the location of the posts which is described above in connection with FIGS. 7-9. Short side 3-8 is that side nearest the output apertures of common arms 15 and 16. The radius of the arc in FIG. 12 is depicted as having a length approximately equal to the long cross-sectional dimension of E-arm aperture 30. The H-arm connection to the junction is depicted by dashed outline showing it being positioned turned at right angles with respect to the E- arm centered about a single axis. It is not a requirement of this embodiment of the invention that the E- and H- arms join the junction along a single axis. The H-arm may be displaced either toward the output end of the arms 15 and 16 or toward closed end 37 with respect to the position of the E-arm. Closed end 37 or at least that portion of it immediately opposite the aperture where the H-arm meets the junction is spaced from the center of the H-arm aperture a distance such that it will act as a shorted tuning stub. Both the E- and Haarm apertures are depicted as containing resonant irises to improve Sample I In one specific embodiment the junction of FIGS. 7 through 9 was made with the following dimensions. The long inside dimension a of each of the arms was .900 inch. The short inside dimension b of the E-arm was .400 inch. The same dimension for the H-arm and the common output arms was .200 inch. The inside width of the junction 0 was 1.850 inches equal to approximately two waveguide widths plus some allowance for septum 25. The distance d from a line drawn crosswise through the center of aperture 30 of the E-arm to the inside surface of end wall 36 is .450 inch. The distance e between posts 27 and 29 along the longitudinal axis of the junction as well as between posts 26 and 28 along the same axis is .305 inch. The distance f between posts 26 and 27 is .962 inch and distance g between posts 28 and 29 is 1.448 inches.

Sample 11 Dimensions of a specific embodiment built in accordance with FIGS. 10 through 12 are as follows. The long inside dimension a of each of the arms was .900 inch. The short inside dimension 1) of the E-arm was .400 inch. The same dimension for the H-arm' and the common output arms was .200 inch. The inside width of the junction c was 1.850 inches equal to approximately two waveguide widths plus some allowance for septum 25. The distance d from a line drawn crosswise through the center of aperture 30 of the E-arm to the inside of end wall 37 is .550 inch. The distance e between posts 27 and 29 along the longitudinal axis of the junction as well as between posts 26 and 28 along the same axis is .305 inch. The distance f between posts 26 and 27 is .962 inch and the distance g between posts 28 and 29 is 1.448 inches.

FIGS. 13 and 14 illustrate graphically the results obtained with the sample embodiments as compared with the analogous prior art embodiments. In each case the E- and H-arm characteristics of the inventive embodiments were nearly the same so the curves apply to both arms. FIG. 13 shows frequency vs. VSWR for a conventional H-plane folded tee in curve 45. This is the curve for the folded tee as illustrated in FIG. 2. Under the same testing conditions a broadband H-plane folded tee in accordance with the embodiment of Sample I and as illustrated in FIGS. 7 through 9 produced curve 46. The inventive junction gave a voltage standing wave ratio better than 1.6 over a bandwidth of 8.2 to 12.40 gigacycles. The bandwidth of the prior art junction within the same voltage standing wave ratio was about 9.7 to 11.3 gigacycles.

The FIG. 14 graph shows frequency vs. VSWR in curve 47 for a prior art folded tee of the type illustrated in FIG. 4. Under the same testing conditions a broadband H-plane folded tee in accordance with the embodiment of Sample II and as illustrated in FIGS. 10 through 12 but with the posts 26-29 located in the preferred positions as described above in connection with FIG. 9 produced curve 48. The junction according to the present invention gave a VSWR better than 1.6 over a bandwidth of 8.2 to 12.40 gigacycles. The bandwidth of the prior art junction within the same VSWR was about 9.0 to 11.20 gigacycles.

While the invention has been described in relation to specific embodiments, various modifications thereof will be apparent to those skilled in the art and it is intended to cover the invention broadly within the spirit and scope of the appended claims.

I claim:

1. An H-plane folded hybrid tee rectangular-waveguide junction comprising an E-plane arm, an H-plane arm, and two common arms folded in an H-plane bounded by their top wide walls in a first common plane and their bottom wide walls in a second common plane, so as to share a common junction region for each said arm bounded by said top and bottom wide walls, and means for matching each said arm at said region so that power fed into the E-plane arm divides into two equal components out of phase in the common arms, power fed into the H-plane arm divides into two equal components in phase in the common arms and power fed into either common arm divides into two equal components in the E-plane arm and the H-plane-arm, wherein the improvement comprises a plurality of inductive posts positioned between the top and bottom wide walls of said common region symmetrically on either side of the E-plane arm in said region for reactively matching said E-plane arm to said common region, and the geometry of an end wall of said region is adjusted for reactively matching said H-plane arm to said common region.

2. An H-plane folded hybrid tee waveguide junction according to claim 1 in which said common arms are folded parallel and share a common narrow wall.

3. An H-plane folded hybrid tee waveguide junction according to claim 1 having at least two said inductive posts in said region on each side of said E-plane arm, positioned to appear to energy propagating from said E-plane arm as two curved waveguide walls extending respectively one from each of the outer narrow walls of said common arms substantially to meet in the vicinity of the narrow side of the E-plane arm further removed from said common arms, for guiding the propagation of wave energy between said E-plane arm and said common arms.

4. An H-plane folded hybrid tee waveguide junction according to claim 2 having at least two said inductive posts in said region on each side of said E-plane arm, the posts on each side of said E-plane arm being positioned in the locus of an are, said posts being sufiiciently close together to appear to energy propagating from said E- plane arm as two arcuately curved waveguide walls extending respectively one from each of the outer narrow walls of said common arms to meet substantially in the vicinity of the narrow side of the E-plane arm further removed from said common arms, said arcs being each curved on the same radius so that said common junction region is electrically equivalent to two. identical H-plane 90 waveguide bends joined at the junction with said E- plane arm to form a 180 bend coupled in the H-plane to said common arms.

5. An H-plane folded hybrid tee waveguide junction according to claim 4 in which said H-plane arm and said common arms are aligned in a single plane.

6. An I-I-plane folded hybrid tee waveguide junction according to claim 4 in which said H-plane arm joins said junction along an axis that is parallel to the axis along which said E-plane arm joins said junction.

7. An H-plane folded hybrid tee waveguide junction according to claim 4 in which said are for each of said 90 bends is curved on a constant radius longer than the distance between the shorter sides of either opening into the bend and centered at a point in the bisector of the planes of said openings such that the length of the portion of said radius within the bend along said bisector is approximately 0.925 of said distance.

8. An H-plane folded hybrid tee waveguide junction according to claim 4 in which said are for each of said 90 bends is curved on a constant radius substantially the same as the distance between the shorter sides of said common arms, each said radius being centered substantially on the same point in said common wall.

9. An H-plane folded hybrid tee waveguide junction according to claim 7 in which one post on each side of said E-plane arm is located at the intersection of the are on which the post is positioned and the extended longitudinal axis of the common arm which is located at said side.

10. An H-plane folded hybrid'tee waveguide junction according to claim 9 in which a second post on each side of said E-plane arm is located at the intersection of the are on which the post is positioned and a line extending across the common junction region substantially perpendicular to the extended longitudinal axes of said common arms and intersecting the longitudinal axis of said E-plane arm extended into said common junction region.

11. An H-plane foldedhybrid tee waveguide junction according to claim 2 in which the remaining narrow walls of said common arms extend straight to meet said end wall at substantially a right angle, and said posts are spaced from said remaining narrow and end walls in said common region.

12. An H-plane folded hybrid tee rectangular-waveguide junction comprising an E-plane arm, an H-plane arm, and two common arms folded in an H-plane bounded by their top wide walls in a first common plane and their bottom wide walls in a second common plane, so as to share a common junction region for each said arm bounded by said top and bottom wide walls, and means for matching each said arm at said region so that power fed into the E-plane arm divides into two equal components out of phase in the common arms, power fed into the H-plane arm divides into two equal components in phase in the common arms and power fed into either common arm divides into two equal components in the E-plane arm and the H-plane arm, wherein the improvement comprises a plurality of electrically inductive means extending between the top and bottom wide walls across said common region symmetrically on either side of the E- plane arm in said region for reactively matching said E- plane arm to said common region, the geometry of an end wall of said region is adjusted for reactively matching said H-plane arm to said common region, said common arms are folded parallel and share a common narrow wall, and the remaining narrow walls of said common arms extend to said end wall to provide an enclosure for said common region which is substantially of uniform electrical width from said common arms to said end wall.

13. An H-plane folded hybrid tee rectangular-waveguide junction comprising an E-plane arm, an H-plane arm, and two common arms folded in an H-plane bounded by their top wide walls in a first common plane and their bottom wide walls in a second common plane, so as to share a common junction region for each said arm bounded by said top and bottom wide walls, and means for matching each said arm at said region so that power fed into the E-plane arm divides into two equal components 180 out of phase in the common arms, power fed into the H-plane arm divides into two equal components in phase in the common arms and power fed into either common arm divides into two equal components in the E- plane arm and the H-plane arm, wherein the improvement comprises electrically conductive means positioned between the top and bottom wide walls of said common region symmetrically on either side of the E-plane arm providing effectively two curved waveguide walls in said region extending respectively one from each of the outer narrow walls of said common arms toward each other in the vicinity of the narrow side of the E-plane arm further removed from said common arms for reactively matching said E-plane arm to said common region, and the geometry of an end wall of said region is adjusted for reactively matching said H-plane arm to said common region.

References Cited UNITED STATES PATENTS 2,806,210 9/1957 Edwards 33311 2,840,787 6/1958 Adcock et al 333-11 HERMAN K. SAALBACH, Primary Examiner.

M. NUSSBAUM, Assistant Examiner. 

12. AN H-PLANE FOLDER HYBRID TEE REECTANGULAR-WAVEGUIDE JUNCTION COMPRISING AN E-PLANE ARM, AN H-PLANE ARM, AND TWO COMMON ARMS FOLDED IN AN H-PLANE BOUNDED BY THEIR TOP WIDE WALLS IN A FIRST COMMON PLANE AND THEIR BOTTOM WIDE WALLS IN A SECOND COMMON PLANE, SO AS TO SHARE A COMMON JUNCTION REGION FOR EACH SAID ARM BOUNDED BY SAID TOP AND BOTTOM WIDE WALLS, AND MEANS FOR MATCHING EACH SAID ARM AT SAID REGION SO THAT POWER FED INTO THE E-PLANE ARM DIVIDES INTO TWO EQUAL COMPONENTS 180* OUT OF PHASE IN THE COMMON ARMS, POWER FED INTO THE H-PLANE ARM DIVIDES INTO TWO EQUAL COMPONENTS IN PHASE IN THE COMMON ARMS AND POWER FED INTO EITHER COMMON ARM DIVIDES INTO TWO EQUAL COMPONENTS IN THE E-PLANE ARM AND THE H-PLANE ARM, WHEREIN THE IMPROVEMENT COMPRISES A PLURALITY OF ELECTRICALLY INDUCTIVE MEANS EXTENDING BETWEEN THE TOP AND BOTTOM WIDE WALLS ACROSS SAID COMMON REGION SYMMETRICALLY ON EITHER SIDE OF THE EPLANE ARM IN SAID REGION FOR REACTIVELY MATCHING SAID EPLANE ARM TO SAID COMMON REGION, THE GEOMETRY OF AN END WALL OF SAID REGION IS ADJUSTED FOR REACTIVELY MATCHING SAID H-PLANE ARM TO SAID COMMON REGION, SAID COMMON ARMS ARE FOLDED PARALLEL AND SHARE A COMMON NARROW WALL, AND THE REMAINING NARROW WALLS OF SAID COMMON ARMS EXTEND TO SAID END WALL TO PROVIDE AN ENCLOSURE FOR SAID COMMON REGION WHICH IS SUBSTANTIALLY OF UNIFORM ELECTRICAL WIDTH FROM SAID COMMON TO SAID END WALL. 